Breeding and Solitary Wave Behavior of Dunes

Beautiful dune patterns can be found in deserts and along coasts due to the instability of a plain sheet of sand under the action of the wind. Barchan dunes are highly mobile aeolian dunes found in areas of low sand availability and unidirectional wind fields. Up to now modelization mainly focussed on single dunes or dune patterns without regarding the mechanisms of dune interactions. We study the case when a small dune bumps into a bigger one. Recently Schwammle et al. and Katsuki et al. have shown that under certain circumstances dunes can behave like solitary waves. This means that they can ``cross'' each other which has been questioned by many researchers before. In other cases we observe coalescence, i.e. both dune merge into one, breeding, i.e. the creation of three baby dunes at the center and horns of a Barchan, or budding, i.e. the small dune, after ``crossing'' the big one, is unstable and splits into two new dunes.